All horses and donkeys belong to the genus Equus but anatomical and behavioural differences exist among species. Equus caballus displays distinctive conformational attributes among breeds provisionally related to ganglion cell distribution and skull and brain morphology. Equus asinus shows less variation in skull shape, and little is known about brain organisation. The current research compared skull and brain morphology between horses and donkeys. Skulls of Equus caballus, primarily of Standardbred type (N=14) and Equus asinus (N=16), were obtained postmortem. All animals had been humanely euthanised for reasons unrelated to this study. Heads were sectioned sagitally along the midline and photographed for measurement of various skull structures using Image J software. Measurements included: skull index (SI)=zygomatic width*100/skull length; cranial index (CI)=cranial width*100/cranial length; nasal index (NI)=zygomatic width*100/nasal length; cranial profile index (CPI)=rectangular area bordered by an 80mm line from orbital notch and occiput; nasal profile index (NPI)= rectangular area bordered by 80mm line from orbital notch and tip of nasal bone; olfactory lobe area (OLA); OL pitch [angle between hard palate and the OL axis]; brain pitch [angle between longitudinal axis of the cerebral hemispheres and the hard palate]; and whorl location (WL) [distance of OL from the level of the forehead whorl]. A General Linear Model determined the main effect of species with Sidak’s multiple comparisons of species’ differences among the various measurements. Donkeys had shorter heads (cranial lengths) than horses (19.7±2.5 vs 23.6±1.4cm respectively; F1,23=51.49, P<0.0002). Donkeys also had smaller cranial widths (13±3.4cm; F1,17=15.91, P<0.001) and mandibular depths (24±2.6cm; F1,21=13.05, P<0.002) than horses (19±0.8 and 27.2±1.1cm, respectively). There was no species difference in SI, ZI, or NI (P>0.40), but donkeys tended to have a smaller CI than horses (F1,17=3.59, P<0.08). Similarly, donkeys had a smaller CPI than horses (F1,21=7.54, P<0.034), but there was no difference in NPI (F1,21=0.05, P>0.83). Donkeys also had a smaller OLA than horses (1.4±0.3 vs 2.3±1.3cm2 respectively; F1,13=4.96, P<0.05) although there was no difference in brain pitch (F1,23=0.69, P>0.43). The greatest difference was seen in WL, which corresponded to the level of the OL in horses, but was extremely rostral in donkeys (F1,21=24.29, P<0.0001). These results show clear differentiation in skull morphology between horses and donkeys which may be linked to behaviour. This may be useful in validating different approaches in the training and management of horses versus donkeys.

Lay person message: Horses demonstrate specific behaviours which may be associated with skull shape, although nothing is known about this relationship in donkeys. This pilot study has shown that donkeys have smaller brain cases and olfactory lobes than Standardbred horses. Donkeys’ facial whorls are located lower down the face while horses’ are in close proximity to the brain’s olfactory lobe. Clarifying differences between horses and donkeys is crucial to understanding species-specific behavioural responses and providing appropriate management and training practices.

Increased levels of personal wealth in China are fuelling demand for luxury products including ejiao, a product made using donkey skin. A traditional medicine, ejiao’s popularity is largely due to its reported anti-aging properties. Demand for donkey skins to produce ejiao is conservatively estimated at 4 million per year. This represents a significant proportion of the global donkey population of 44 million. China’s own donkey population has nearly halved in the last 20 years and entrepreneurs are now looking worldwide to satisfy a growing demand. Despite their essential role in livelihoods and 30 community resilience donkeys are largely invisible in livestock policies, livelihoods and humanitarian projects. It is therefore unsurprising that the emerging trade in skins is also invisible. Donkeys are frequently stolen from owners across Africa and illegally slaughtered in the bush; only the skins are removed and carcasses left to rot. In other areas, donkeys are bought at less than current market value and are transported in inhumane conditions to recently built legal slaughterhouses. In the short term donkey owners are facing donkey prices that have increased up to tenfold within a few years and they are without the means to replace animals they depend on. The invisibility of the trade is compounded by illegitimate export practices and criminal gangs. Due to the lucrative market for skins intensive farms are present in China and are likely to expand to other countries. Such rearing creates significant welfare concerns for a species poorly adapted to intensive practices. Australia has been exploring harvesting feral donkeys in the Northern Territories, possibly including some considered by indigenous communities to be owned and with cultural significance. This demand risks the welfare of donkeys, the communities who live with them, and, within a few decades, perhaps the species as a whole.